Your gardening questions answered: Is it too late to get rid of this vigorous pest?

Q: Some time ago I planted a number of Tropaeolum ciliatum along a privet hedge. Over the years it has covered the hedge and is now choking it, and has spread to planting on the adjacent road.

Is there any way I can get rid of the pest? Please don’t reply using two of the saddest words in the English language: “too late”! RM, Co Down

A: Many gardeners are aware of the dangers of plants such as Japanese knotweed and bindweed, species that were originally introduced into cultivation in this country as garden ornamentals before the threat that they posed as invasive species was realised. But your dilemma serves as a cautionary tale and a powerful reminder of the threat that some other non-native invasive species continue to pose to unsuspecting gardeners.

A native of Chile, Tropaeolum ciliatum can still easily be found for sale (both its seed and as a young plant), where it’s often described as a “vigorous” perennial climbing nasturtium that’s recommended for growing up through large shrubs, trees, hedges or along a fence or pergola.

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Its abundance of pretty yellow flowers, decorative foliage, hardiness and ability to tolerate shade, make it sound like a great choice. But in fact, it’s proven itself to be a highly invasive, rampant species that can easily outcompete many other decorative species and should be studiously avoided.

I’m very sorry to use the words “too late” but you’re absolutely correct in suspecting that eradicating it from your garden will be a huge challenge.

Digging out its tuberous root system would be impossible, so while I generally hate to recommend the use of weedkiller, in this case its repeated use will be necessary. Just make sure to pull the plant’s slim, long stems away from your hedge before treatment to avoid damaging the latter.